This invention relates to an improved lubricating oil composition which is particularly useful as a lubricant in marine applications and particularly as a marine cylinder lubricant (MDCL). More particularly, this invention relates to a finished lubricant formulation exhibiting improved ring wear and liner wear performance which employ certain amounts of borated dispersants and zinc compounds.
The present invention is based upon the discovery that the incorporation of certain amounts of borated dispersants such as polyisobutenyl succinic anhydride-polyamine borated derivatives into a lubricating oil composition in combination with certain amounts of zinc dialkyl dithiophosphate antiwear additives in MDCL formulations give surprising wear results particularly in cylinder liner and piston ring wear. Combinations of borated dispersants and zinc antiwear additives are known in lubricants for automobile engines, but have not been described in compositions suitable for marine diesels lubricants. GB Pat. No. 1054310 describes nitrogen- and boron-containing compositions comprising borated dispersants such as polyisobutenyl succinic anhydride - polyamine borated derivatives and their use in gasoline and diesel engines including use as MDCL. The use of such borated dispersants in combination with zinc dialkyl dithiophosphate antiwear additives in general is disclosed, but there is no disclosure of a combination of borated dispersant and zinc antiwear additive in a formulation having the viscosity and total base number appropriate for MDCL.